Migrating model syncing to a (static) class, rather than flat functions shared through settings.py
Migrating model syncing to a (static) class, rather than flat functions shared through settings.py.  Similar for device_counting.
Merge branch 'syncing_models' of github.com:bcipolli/ka-lite into syncing_models

Conflicts:
	kalite/securesync/models.py
Merge remote-tracking branch 'origin/syncing_models' into syncing_errors_bug

Conflicts:
	kalite/settings.py
Propagating syncing errors, reporting errors and exceptions to user
propagate server error information to client
Merge remote-tracking branch 'upstream/develop' into syncing_models
separated out model_sync code, removed static class.  Made other small changes based on code review
Blocking bug fixes: removing class function parameter, importing global var (json_serializer)
now fixing that json_serializer bug, but WITH testing.  Woot\! :P
separating files caused double-dependency; resolving with in-function imports
enable syncing across different KA Lite versions with different schemas--central server side
updated to modify directly in django code; this is necessary for Deserialization (rather than copying Django code)
making errors robust, testing that central server with old version can import models with new fields (and successfully ignore just those fields)
starting to document package tweaks
fixing bugs in registration interaction; using a single deserializer object in each module
fixing a tweak; serializers don't deserialize.
backing out common serializer change; walking through each serialize/deserialize function call to validate proper args are passed
Fixing bug with failed import (caught by downstream tests--woot!!
more consistent naming of views